Ultraviolet c light-emitting diode

ABSTRACT

An ultraviolet C light-emitting diode including an n-type semiconductor layer, a p-type semiconductor layer, an active layer, a two-dimensional hole gas (2DHG) inducing layer, and an electron blocking layer is provided. The active layer is disposed between the n-type semiconductor layer and the p-type semiconductor layer, wherein a wavelength of a maximum peak of a spectrum emitted by the active layer ranges from 230 nm to 280 nm. The two-dimensional hole gas (2DHG) inducing layer is disposed between the active layer and the p-type semiconductor layer. A concentration of magnesium in the 2DHG inducing layer is less than 1017 atoms/cm3. The electron blocking layer is disposed between the p-type semiconductor layer and the 2DHG inducing layer. A concentration of magnesium in a part of the electron blocking layer adjacent to the 2DHG inducing layer is greater than 1019 atoms/cm3.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part (CIP) application of andclaims the priority benefit of U.S. application Ser. No. 16/431,748,filed on Jun. 5, 2019, now pending, which claims the priority benefit ofTaiwan application serial no. 107145438, filed on Dec. 17, 2018. Theentirety of each of the above-mentioned patent applications is herebyincorporated by reference herein and made a part of this specification.

TECHNICAL FIELD

The technical field relates to an ultraviolet C light-emitting diode.

BACKGROUND

In order to make an electron hole carrier to be easily injected into alight-emitting layer, active layer or multiple-quantum well (MQW), anelectron blocking layer (EBL) in an ultraviolet C light-emitting diode(UVC-LED) structure is doped with beryllium, magnesium or zinc, etc. toform a p-type semiconductor. In this way, in addition to increasing theelectron hole concentration, the efficiency of the ultraviolet Clight-emitting diode element can be further improved.

However, when the electron blocking layer is doped with beryllium,magnesium or zinc, etc., since the concentration of aluminum in theelectron blocking layer is greater than the concentration of aluminum inthe quantum barrier in the light-emitting layer, active layer ormultiple-quantum well (MQW), it is not easy for beryllium, magnesium orzinc, etc. to be doped. On the other hand, if the doping amount ofberyllium, magnesium or zinc, etc. is increased, the problem of memoryeffect of beryllium, magnesium, zinc, etc. and its diffusion into thequantum well or quantum barrier will be caused. As a result, excessiveimpurities may form defects in the quantum well or quantum barrier,resulting in a decrease in the luminous efficiency of the ultraviolet Clight-emitting diode device and an unnecessary defect illumination.

SUMMARY

An embodiment of the disclosure provides an ultraviolet C light-emittingdiode including an n-type semiconductor layer, a p-type semiconductorlayer, an active layer, a first electron blocking layer and a secondelectron blocking layer. The active layer is located between the n-typesemiconductor layer and the p-type semiconductor layer, and thewavelength of the maximum peak of the spectrum emitted by the activelayer ranges from 230 nm to 280 nm, and the concentration of magnesiumin the active layer is less than 10¹⁷ atoms/cm³. The first electronblocking layer and the second electron blocking layer are locatedbetween the p-type semiconductor layer and the active layer, theconcentration of magnesium in the second electron blocking layer isgreater than the concentration of magnesium in the first electronblocking layer, and the concentration of magnesium in the secondelectron blocking layer is greater than 10¹⁸ atoms/cm³.

An embodiment of the disclosure provides an ultraviolet C light-emittingdiode including an n-type semiconductor layer, a p-type semiconductorlayer, an active layer, a two-dimensional hole gas (2DHG) inducinglayer, and an electron blocking layer. The active layer is disposedbetween the n-type semiconductor layer and the p-type semiconductorlayer, wherein a wavelength of a maximum peak of a spectrum emitted bythe active layer ranges from 230 nm to 280 nm. The two-dimensional holegas (2DHG) inducing layer is disposed between the active layer and thep-type semiconductor layer. A material of the 2DHG inducing layerincludes Al_(α)Ga_(β)N, wherein β=1−α, and a concentration of magnesiumin the 2DHG inducing layer is less than 10¹⁷ atoms/cm³. The electronblocking layer is disposed between the p-type semiconductor layer andthe 2DHG inducing layer. A material of the electron blocking layerincludes Al_(γ)Ga_(δ)N, wherein δ=1−γ, 0.65<γ≤0.9, and a concentrationof magnesium in a part of the electron blocking layer adjacent to the2DHG inducing layer is greater than 10¹⁹ atoms/cm³. The ultraviolet Clight-emitting diode satisfies α>γ and 0.1<α−γ≤0.3, so that 2DHG isformed at an interface between the 2DHG inducing layer and the electronblocking layer.

Several exemplary embodiments accompanied with figures are described indetail below to further describe the disclosure in details.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide further understanding,and are incorporated in and constitute a part of this specification. Thedrawings illustrate exemplary embodiments and, together with thedescription, serve to explain the principles of the disclosure.

FIG. 1 is a schematic cross-sectional view of an ultraviolet Clight-emitting diode according to an embodiment of the disclosure.

FIG. 2 is a diagram showing the ingredient distribution of theultraviolet C light-emitting diode of FIG. 1 measured by a secondary ionmass spectrometer.

FIG. 3 is a spectrum diagram of the ultraviolet C light-emitting diodeof FIG. 1.

FIG. 4 is an energy band diagram of an ultraviolet C light-emittingdiode in a comparative example.

FIG. 5 is an energy band diagram of the ultraviolet C light-emittingdiode of FIG. 1.

FIG. 6 is a schematic cross-sectional view showing an ultraviolet Clight-emitting diode according to another embodiment of the disclosure.

FIG. 7 is a diagram showing the ingredient distribution of anultraviolet C light-emitting diode of a comparative example measured bya secondary ion mass spectrometer.

FIG. 8 is a spectrum diagram of the ultraviolet C light-emitting diodein comparative example of FIG. 7.

FIG. 9 is a diagram showing the ingredient distribution of anultraviolet C light-emitting diode of another embodiment of thedisclosure measured by a secondary ion mass spectrometer.

FIG. 10 is a spectrum diagram of an ultraviolet C light-emitting diodeof the embodiment corresponding to FIG. 9.

FIG. 11 is a schematic cross-sectional view showing an ultraviolet Clight-emitting diode according to yet another embodiment of thedisclosure.

FIG. 12 is a schematic cross-sectional view showing an ultraviolet Clight-emitting diode according to still another embodiment of thedisclosure.

FIG. 13 is a schematic cross-sectional view showing an ultraviolet Clight-emitting diode according to yet still another embodiment of thedisclosure.

FIG. 14 is a diagram showing the ingredient distribution of theultraviolet C light-emitting diode of FIG. 13 measured by a secondaryion mass spectrometer.

FIG. 15 is an energy band diagram of the ultraviolet C light-emittingdiode of FIG. 13.

FIG. 16A is a curve of carrier injection efficiency of the ultraviolet Clight-emitting diode of FIG. 13 with respect to α−γ when the electronblocking layer has a Mg concentration of 10¹⁹ atoms/cm³.

FIG. 16B is a curve of carrier injection efficiency of the ultraviolet Clight-emitting diode of FIG. 13 with respect to α−γ when the electronblocking layer has a Mg concentration of 10¹⁹ atoms/cm³.

FIG. 17 is an image of transmission electron microscopy (TEM) of theultraviolet C light-emitting diode in FIG. 13.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic cross-sectional view of an ultraviolet Clight-emitting diode according to an embodiment of the disclosure.Referring to FIG. 1, the ultraviolet C light-emitting diode 100 of thepresent embodiment includes an n-type semiconductor layer 110, a p-typesemiconductor layer 120, an active layer or a multiple-quantum well 130,and an electron blocking layer 200. The n-type semiconductor layer 110is, for example, an n-type aluminum gallium nitride layer, which mayhave a doping source (for example, carbon or silicon) of group IVAelement, and the doping source of the group IVA element is used toreplace aluminum or gallium atoms, and thus generating additional freeelectrons, or may have a doping source of group VIA element, the dopingsource of the group VIA element is used to replace the nitrogen atom,and thus generating additional free electrons, or may have a dopingsource of other elements, which replaces aluminum, gallium, and nitrogenand exhibits the feature of generating additional free electrons. Inthis embodiment, the ultraviolet C light-emitting diode 100 furtherincludes a sapphire substrate 160, an aluminum nitride template layer170, a buffer layer 180, and an unintentionally doped aluminum galliumnitride layer 190, wherein the aluminum nitride template layer 170, thebuffer layer 180, the unintentionally doped aluminum gallium nitridelayer 190, and the n-type semiconductor layer 110 are sequentiallystacked on the sapphire substrate 160. The material of the buffer layer180 is, for example, aluminum gallium nitride, and the cationic molarfraction of aluminum ranges from 95% to 50%, and the cationic molarfraction of gallium ranges from 5% to 50%. Alternatively, the bufferlayer 180 may be an aluminum gallium nitride layer having a superlatticestructure, of which the cationic molar fraction of aluminum ranges from95% to 50%, and the cationic molar fraction of gallium ranges from 5% to50%.

In the present embodiment, the n-type semiconductor layer 110 includes afirst n-type aluminum gallium nitride layer 112 and a second n-typealuminum gallium nitride layer 114, wherein the n-type dopingconcentration of the first n-type aluminum gallium nitride layer 112 ishigher than the n-type doping concentration of the second n-typealuminum gallium nitride layer 114, and the second n-type aluminumgallium nitride layer 114 and the first n-type aluminum gallium nitridelayer 112 are sequentially stacked on the unintentionally doped aluminumgallium nitride layer 190.

The active layer 130 is a light-emitting layer. In the embodiment, theactive layer 130 is a multiple-quantum well (MQW) layer including aplurality of barrier layers 132 and a plurality of well layers 134stacked alternately on the n-type semiconductor layer 110. In thisembodiment, the material of both of the barrier layer 132 and the welllayer 134 is aluminum gallium nitride, except that the aluminumconcentration in the barrier layer 132 is higher than that in the welllayer 134.

The electron blocking layer 200 includes a first electron blocking layer210 and a second electron blocking layer 220. In this embodiment, thefirst electron blocking layer 210 and the second electron blocking layer220 are sequentially stacked on the active layer 130. The first electronblocking layer 210 and the second electron blocking layer 220 are, forexample, aluminum gallium nitride layers doped with magnesium, whereinthe concentration of magnesium in the second electron blocking layer 220is greater than the concentration of magnesium in the first electronblocking layer 210, and the concentration of magnesium in the secondelectron blocking layer 220 is greater than 10¹⁸ atoms/cm³.

The p-type semiconductor layer 120 is stacked on the electron blockinglayer 200. In this embodiment, the p-type semiconductor layer 120includes a first p-type gallium nitride or aluminum gallium nitridelayer 122 and a second p-type gallium nitride or aluminum galliumnitride layer 124 sequentially stacked on the electron blocking layer200, wherein the p-type doping concentration of the second p-typegallium nitride or aluminum gallium nitride layer 124 is higher than thep-type doping concentration of the first p-type gallium nitride oraluminum gallium nitride layer 122. The p-type dopant in the firstp-type gallium nitride or aluminum gallium nitride layer 122 and thesecond p-type gallium nitride or aluminum gallium nitride layer 124 maybe a group IIA element, such as beryllium or magnesium, and magnesium isused in the embodiment.

In this embodiment, the active layer 130 is disposed between the n-typesemiconductor layer 110 and the p-type semiconductor layer 120, and thewavelength of the maximum peak of the spectrum emitted by the activelayer 130 ranges from 230 nm to 280 nm, that is, falling within thewavelength band of ultraviolet C. The ultraviolet wavelength bandincludes ultraviolet A (UVA) band, ultraviolet B (UVB) band andultraviolet C (UVC) band. The wavelength of the ultraviolet A bandranges about from 400 nm to 315 nm, that is, its photon energy range isabout 3.10 eV to 3.94 eV. The wavelength of ultraviolet B band rangesabout from 315 nm to 280 nm, that is, its photon energy range is about3.94 eV to 4.43 eV. The wavelength of ultraviolet C band ranges aboutfrom 280 nm to 100 nm, that is, its photon energy range is about 4.43 eVto 12.4 eV. The concentration of magnesium in the active layer 130 isless than 10¹⁷ atoms/cm³. Further, the first electron blocking layer 210and the second electron blocking layer 220 are located between thep-type semiconductor layer 120 and the active layer 130. In theembodiment, the second electron blocking layer 220 is located betweenthe first electron blocking layer 210 and the p-type semiconductor layer120.

The ultraviolet C light-emitting diode 100 of the embodiment may furtherinclude a first electrode 50 and a second electrode 60, wherein thefirst electrode 50 is electrically connected to the n-type semiconductorlayer 110, and the second electrode 60 is electrically connected to thep-type semiconductor layer 120. By applying a forward bias to the firstelectrode 50 and the second electrode 60, the active layer 130 of theultraviolet C light-emitting diode 100 can emit an ultraviolet C band byradiative recombination. In FIG. 1, the first electrode 50 and thesecond electrode 60 are exemplified in the form of horizontalarrangement, that is, the first electrode 50 and the second electrode 60are located on the same side of the ultraviolet C light-emitting diode100. However, in other embodiments, the first electrode 50 and thesecond electrode 60 may also be in a vertical configuration, that is,the first electrode 50 is located below the n-type semiconductor layer110, and the second electrode 60 is located above the p-typesemiconductor layer 120.

In the ultraviolet C light-emitting diode 100 of the present embodiment,since it is designed that the concentration of magnesium in the secondelectron blocking layer 220 is greater than the concentration ofmagnesium in the first electron blocking layer 210, and theconcentration of magnesium in the second electron blocking layer 220 isgreater than 10¹⁸ atoms/cm³, the doping of magnesium in a specific ratiorelationship can effectively suppress the electrons in the active layer130 from overflowing to the p-type semiconductor layer 120, therebyimproving the device performance of the ultraviolet C light-emittingdiode 100. In addition, in the ultraviolet C light-emitting diode 100 ofthe present embodiment, with the adjustment of appropriate cationicmolar fraction of aluminum and the appropriate doping amount ofmagnesium in the electron blocking layer 200, not only that it ispossible to prevent the electrons from overflowing to the p-typesemiconductor layer 120, but also the efficiency of injecting the holecarriers into the active layer 130 can be improved, thereby increasingthe luminous efficiency of the ultraviolet C light-emitting diode 100.

In this embodiment, the thickness T2 of the second electron blockinglayer 220 falls within a range of 0.1 nm to 20 nm, and the thickness T1of the first electron blocking layer 210 falls with a range of 10 nm to100 nm.

FIG. 2 is a diagram showing the ingredient distribution of theultraviolet C light-emitting diode of FIG. 1 measured by a secondary ionmass spectrometer (SIMS). FIG. 3 is a spectrum diagram of theultraviolet C light-emitting diode of FIG. 1. Referring to FIG. 1 toFIG. 3, the spectrum of the light emitted by the ultraviolet Clight-emitting diode 100 of the present embodiment includes a firstlight-emitting peak P1 and a second light-emitting peak P2, and thespectral intensity of the first light-emitting peak P1 is 20 or moretimes the spectral intensity of the second light-emitting peak P2. InFIG. 3, the second light-emitting peak P2 is not obvious, but if alogarithm value is taken from the vertical axis (i.e., spectralintensity), the second light-emitting peak P2 is clearly shown, which isbecause that the magnitude of the difference between the spectralintensity of the first light-emitting peak P1 and the spectral intensityof the second light-emitting peak P2 is too large so that the secondlight-emitting peak P2 cannot be seen in FIG. 3, but the secondlight-emitting peak P2 becomes obvious after a logarithm value is takenfrom the vertical axis. In the present embodiment, the differenceobtained by subtracting the wavelength of the first light-emitting peakP1 from the wavelength of the second light-emitting peak P2 falls withinthe range of 20 nm to 40 nm. The second light-emitting peak P2 isgenerated by the defect illumination. In FIG. 3, it is apparently to beseen that the defect illumination of the ultraviolet C light-emittingdiode 100 of the present embodiment is well suppressed, so theultraviolet C light-emitting diode 100 has good luminous efficiency.

In the present embodiment, the highest concentration (for example, theconcentration of magnesium at point Q1 in FIG. 2) of magnesium in thesecond electron blocking layer 220 is 5 to 200 times the lowestconcentration (for example, the concentration of magnesium at point Q2in FIG. 2) of magnesium in the first electron blocking layer 210, and is20 to 80 times in another embodiment. Further, in the presentembodiment, the concentration of magnesium in the second electronblocking layer 220 is ½ to 1/50 times the concentration of magnesium inthe p-type semiconductor layer 120. In addition, in the presentembodiment, a distribution curve of the whole concentration of magnesiumin the first electron blocking layer 210 and the second electronblocking layer 220 from the p-type semiconductor layer 120 to the activelayer 130 is steep-down at the beginning and then flattened and finallysteep-down as shown in FIG. 2.

In this embodiment, the cationic molar fraction of aluminum in the firstelectron blocking layer 210 and the second electron blocking layer 220falls within a range of 60% to 80%. For example, when the chemicalformula of the main ingredient of the first electron blocking layer 210and the second electron blocking layer 220 can be expressed asAl_(x)Ga_(1-x)N, then x in the chemical formula is the cationic molarfraction of aluminum.

In the present embodiment, the refractive index of the second electronblocking layer 220 is smaller than the refractive index of the welllayer 134 of the active layer 130 and smaller than the refractive indexof the barrier layer 132 of the active layer 130. In addition, therefractive index of the first electron blocking layer 210 is alsosmaller than the refractive index of the well layer 134 of the activelayer 130 and smaller than the refractive index of the barrier layer 132of the active layer 130. In general, in the material of aluminum galliumnitride, the higher the content of aluminum, the smaller the refractiveindex.

In the ultraviolet C light-emitting diode 100 of the present embodiment,since the second electron blocking layer 220 is located between thefirst electron blocking layer 210 and the p-type semiconductor layer120, the magnesium can be effectively doped in the second electronblocking layer 220 such that the magnesium is not diffused into theactive layer 130 in a gradient distribution. In this way, the defectillumination induced by the magnesium entering the active layer 130 canbe effectively reduced, thereby improving the luminous efficiency of theultraviolet C light-emitting diode 100. In the present embodiment, theluminous intensity or the light output power of the ultraviolet Clight-emitting diode 100 is 17.4 mW.

FIG. 4 is an energy band diagram of an ultraviolet C light-emittingdiode in a comparative example. FIG. 5 is an energy band diagram of theultraviolet C light-emitting diode of FIG. 1. Referring to FIG. 1, FIG.4 and FIG. 5, the structures of the ultraviolet C light-emitting diodescorresponding to FIG. 4 and FIG. 5 may be the same as the structure ofthe ultraviolet C light-emitting diode 100 of FIG. 1. The differencebetween the two is that the concentration of magnesium in the electronblocking layer 200 in FIG. 4 is about 5×10¹⁷ atoms/cm³, and theconcentration of magnesium in the electron blocking layer 200 in FIG. 5is about 5×10¹⁸ atoms/cm³. In FIG. 4 and FIG. 5, the curve correspondingto E_(c) is the lowest energy level of the conduction band, the curvecorresponding to Ef_(n) is the quasi-fermi energy level of the electron,the curve corresponding to E_(v) is the highest energy level of thevalence band, and the curve corresponding to Ef_(p) is the quasi-fermienergy level of the hole. As shown in FIG. 4 and FIG. 5, when theconcentration of magnesium in the electron blocking layer 200 is high,the conduction band barrier height difference (ΔE_(c)) betweenconduction band barrier height of the second electron blocking layer 220and the conduction band barrier height of the active layer 130 islarger, and the larger the effective conduction band barrier heightdifference (ΔE_(c)), the electrons from the active layer 130 are lesslikely to overflow to the p-type semiconductor layer 120. In theembodiment of FIG. 1, the conduction band barrier formed by the secondelectron blocking layer 220 is 0.2 to 1 eV higher than the conductionband barrier formed by the active layer 130, thereby the effectiveconduction band barrier height difference (ΔE_(c)) is 0.2 to 1 eV, whichcan effectively blocking the electrons from the active layer 130 fromoverflowing to the p-type semiconductor layer 120, thus effectivelyavoiding a decrease in luminous efficiency caused by the overflow of theelectrons.

FIG. 6 is a schematic cross-sectional view showing an ultraviolet Clight-emitting diode according to another embodiment of the disclosure.FIG. 7 is a diagram showing the ingredient distribution of anultraviolet C light-emitting diode of a comparative example measured bya secondary ion mass spectrometer. FIG. 8 is a spectrum diagram of theultraviolet C light-emitting diode in comparative example of FIG. 7.Referring to FIG. 6 first, the ultraviolet C light-emitting diode 100 aof the present embodiment is similar to the ultraviolet C light-emittingdiode 100 of FIG. 1, and the difference between the two is described asfollows. In the ultraviolet C light-emitting diode 100 a of the presentembodiment, the second electron blocking layer 220 of the electronblocking layer 200 a is located between the first electron blockinglayer 210 and the active layer 130. In this embodiment, the thickness T2a of the second electron blocking layer 220 falls within a range of 0.1nm to 10 nm, and the thickness T1 of the first electron blocking layer210 falls within a range of 10 nm to 100 nm.

Referring to FIG. 7 and FIG. 8 again, in this comparative example, ascan be seen from FIG. 7, since the cationic molar fraction of aluminumin the active layer 130 is lower than that of the electron blockinglayer 200, the magnesium ions in the second electron blocking layer 220are easily diffused into the active layer 130 in a gradient distributionto cause defect illumination, and the second light-emitting peak P2 isthus more obvious in the spectrum diagram of FIG. 8. As a result, theluminous intensity or the light output power of the ultraviolet Clight-emitting diode 100 a of the comparative example became 5.4 mW. Inorder to reduce the diffusion of magnesium ions in the second electronblocking layer to the active layer 130 to cause defect illumination, inanother embodiment of the disclosure, the electron blocking layer 200may have a magnesium concentration distribution as shown in FIG. 9, thatis, magnesium is doped in the electron blocking layer 200 in a specificdoping ratio relationship to make magnesium less diffuse into the activelayer 130 (please compare the concentration of magnesium in the activelayer 130 in FIG. 7 and FIG. 9). On this occasion, it was found thatsuch magnesium concentration distribution less causes defectillumination, and the second light-emitting peak P2 in the correspondingspectrum (shown in FIG. 10) is effectively suppressed and is notobvious, and is hardly seen. That is, this embodiment succeeds in makingthe luminous intensity of the first light-emitting peak P1 to be largerthan 20 times the defect luminous intensity of the second light-emittingpeak P2.

FIG. 11 is a schematic cross-sectional view showing an ultraviolet Clight-emitting diode according to yet another embodiment of thedisclosure. Referring to FIG. 11, the ultraviolet C light-emitting diode100 b of the present embodiment is similar to the ultraviolet Clight-emitting diode 100 of FIG. 1, and the difference between the twois described as follows. In the ultraviolet C light-emitting diode 100 bof the present embodiment, the second electron blocking layer 220 of theelectron blocking layer 200 b is located in the first electron blockinglayer 210. In the present embodiment, the thickness T2 b of the secondelectron blocking layer 220 falls within the range of 0.1 nm to 15 nm,and the thickness (that is, the thickness T11 plus the thickness T12 inFIG. 11) of the first electron blocking layer 210 falls within the rangeof 10 nm to 100 nm.

FIG. 12 is a schematic cross-sectional view showing an ultraviolet Clight-emitting diode according to still another embodiment of thedisclosure. Referring to FIG. 12, the ultraviolet C light-emitting diode100 c of the present embodiment is similar to the ultraviolet Clight-emitting diode 100 of FIG. 1, and the difference between the twois described as follows. In the electron blocking layer 200 c of theultraviolet C light-emitting diode 100 c of the present embodiment, thefirst electron blocking layer 210 c has a superlattice structure.Specifically, the first electron blocking layer 210 c has a plurality offirst sub-layers 212 and a plurality of second sub-layers 214 that arealternately stacked, and the first sub-layers 212 and the secondsub-layers 214 are both aluminum gallium nitride layers doped withmagnesium, but the concentration of aluminum in the first sub-layers 212is different from the concentration of aluminum in the second sub-layers214. That is, the concentration of aluminum in the first electronblocking layer 210 c is alternately changed up and down from the sideclose to the active layer 130 to the side close to the p-typesemiconductor layer 120.

In contrast, in the embodiments of FIG. 2, FIG. 7, and FIG. 9, theconcentration of aluminum of the first electron blocking layer 210 nearthe p-type semiconductor layer 120 is less than the concentration ofaluminum of the first electron blocking layer 210 near the active layer130, for example, the concentration of aluminum in the first electronblocking layer 210 gradually increases from the side close to the p-typesemiconductor layer 120 toward the active layer 130, and the aluminumconcentration difference between the aluminum concentration of the firstelectron blocking layer 210 near the p-type semiconductor layer 120 andthe aluminum concentration of the first electron blocking layer 210 nearthe active layer 130 is about 5% cationic molar fraction. Theconcentration of gallium in the first electron blocking layer 210 nearthe p-type semiconductor layer 120 is greater than the concentration ofgallium in the first electron blocking layer 210 near the active layer130, and the gallium concentration difference between the galliumconcentration of the first electron blocking layer 210 near the p-typesemiconductor layer 120 and the gallium concentration of the firstelectron blocking layer 210 near the active layer 130 is about 5%cationic molar fraction.

In addition, in the embodiment of FIG. 12, the second electron blockinglayer 220 may be disposed between the first electron blocking layer 210c and the active layer 130 or disposed in the first electron blockinglayer 210 c.

FIG. 13 is a schematic cross-sectional view showing an ultraviolet Clight-emitting diode according to yet still another embodiment of thedisclosure. Referring to FIG. 13, an ultraviolet C light-emitting diode100 d in this embodiment is similar to the ultraviolet C light-emittingdiode 100 a in FIG. 6, and the main difference therebetween is asfollows. In this embodiment, the ultraviolet C light-emitting diode 100d further includes a two-dimensional hole gas (2DHG) inducing layer 140disposed between the active layer 130 and the p-type semiconductor layer120 d. The electron blocking layer 200 d is disposed between the p-typesemiconductor layer 120 d and the 2DHG inducing layer 140. The materialof the 2DHG inducing layer 140 includes Al_(α)Ga_(β)N, wherein β=1−α,and 0.7<α≤0.95, where a is the cationic molar fraction of aluminum inthe compound Al_(α)Ga_(β)N, and β is the cationic molar fraction ofgallium in the compound Al_(α)Ga_(β)N. The concentration of magnesium inthe 2DHG inducing layer 140 is less than 10¹⁷ atoms/cm³. In anembodiment the concentration of magnesium in the active layer 130 isless than 10¹⁷ atoms/cm³. The material of the electron blocking layer200 d includes Al_(γ)Ga_(δ)N, wherein δ=1−γ, and 0.65<γ≤0.9, where γ isthe cationic molar fraction of aluminum in the compound Al_(γ)Ga_(δ)N,and δ is the cationic molar fraction of gallium in the compoundAl_(γ)Ga_(δ)N.

The concentration of magnesium in the part of the electron blockinglayer 200 d adjacent to the 2DHG inducing layer 140 is greater than 10¹⁹atoms/cm³, or is greater than 10²⁰ atoms/cm³ in an embodiment. Theultraviolet C light-emitting diode 100 d satisfies α>γ and 0.1<α−γ≤0.3.The aluminum concentration of the 2DHG inducing layer 140 is greaterthan the aluminum concentration of the electron blocking layer 200 d.The aluminum concentration difference between the 2DHG inducing layer140 and the electron blocking layer 200 d will induce 2DHG formed byspontaneous polarization and piezo polarization at the interface betweenthe 2DHG inducing layer 140 and the electron blocking layer 200 d. Theinduction of 2DHG facilitates electron holes to be directly injectedinto the active layer 130, so that the light efficiency of theultraviolet C light-emitting diode 100 d is effectively improved. Byadopting the 2DHG inducing layer 140, the light output power of theultraviolet C light-emitting diode 100 d is improved by 56%. The lightoutput power of packaged LED is improved from 17 mW (without the 2DHGinducing layer 140) to 26 mW (with the 2DHG inducing layer 140).

In this embodiment, the electron blocking layer 200 d includes a firstelectron blocking layer 210 d and a second electron blocking layer 220d, wherein the second electron blocking layer 220 d is disposed betweenthe 2DHG inducing layer 140 and the first electron blocking layer 210 d.The concentration of magnesium in the second electron blocking layer 220d is greater than the concentration of magnesium in the first electronblocking layer 210 d, and the concentration of magnesium in the secondelectron blocking layer 220 d is greater than 10¹⁹ atoms/cm³, or isgreater than 10²⁰ atoms/cm³ in an embodiment. That is, the secondelectron blocking layer 220 d is the aforementioned part of the electronblocking layer 200 d adjacent to the 2DHG inducing layer 140.

In this embodiment, the 2DHG inducing layer 140 is in contact with oneof the well layers 134 closest to the 2DHG inducing layer 140. In thisembodiment, the thickness T4 of the 2DHG inducing layer 140 ranges from1 nm to 3 nm. In this embodiment, the ratio of the thickness T3 of theelectron blocking layer 200 d to the thickness T4 of the 2DHG inducinglayer 140 ranges from 6 to 20. In an embodiment, the thickness T4 of the2DHG inducing layer 140 ranges from 1 nm to 3 nm, and the thickness T3of the electron blocking layer 200 d ranges from 20 nm to 60 nm, forexample.

For light emitted by the active layer 130, the transparency of the 2DHGinducing layer 140 may be greater than the transparency of the electronblocking layer 200 d. In this embodiment, for the light emitted by theactive layer 130, the transparency of the 2DHG inducing layer 140 isgreater than the transparency of the n-type semiconductor layer 110, andthe transparency of the n-type semiconductor layer 110 is less than thetransparency of the electron blocking layer 200 d.

Besides, the refractive index of the 2DHG inducing layer 140 may be lessthan the refractive index of the electron blocking layer 200 d. Therefractive index of the 2DHG inducing layer 140 is less than therefractive index of n-type semiconductor layer 110. Moreover, theelectrical resistivity of the 2DHG inducing layer 140 may be greaterthan the electrical resistivity of the electron blocking layer 200 d.The electrical resistivity of the 2DHG inducing layer 140 may be greaterthan the electrical resistivity of the n-type semiconductor layer 110.In addition, the aluminum concentration of the 2DHG inducing layer 140may be greater than the aluminum concentration of the n-typesemiconductor layer 110. Moreover, the gallium concentration of the 2DHGinducing layer 140 is less than the gallium concentration of electronblocking layer 200 d, and is less than the gallium concentration of then-type semiconductor layer 110. In an embodiment, the aluminumconcentration of the electron blocking layer 200 d is greater than orequal to the aluminum concentration of the well layers 134. In anembodiment, the aluminum concentration of the electron blocking layer200 d is greater than or equal to the aluminum concentration of thebarrier layers 132.

In this embodiment, the p-type semiconductor layer 120 d includes analuminum grading layer 122 d and a p-type semiconductor sub-layer 124 d,wherein the p-type semiconductor sub-layer 124 d is, for example, amagnesium-doped gallium nitride layer, and the aluminum grading layer122 d is, for example, a magnesium-doped aluminum gallium nitride layerwith aluminum concentration gradually decreasing from the side close tothe electron blocking layer 200 d to the side close to the p-typesemiconductor sub-layer 124 d.

FIG. 14 is a diagram showing the ingredient distribution of theultraviolet C light-emitting diode of FIG. 13 measured by a secondaryion mass spectrometer (SIMS). The unit “c/s” in FIG. 14 means counts persecond. Referring to FIG. 13 and FIG. 14, in the embodiment of FIG. 14,a of Al_(α)Ga_(β)N of the 2DHG inducing layer 140 is, for example, 0.95.The Mg concentration of the 2DHG inducing layer 140 is less than 10¹⁷atoms/cm³, and the Mg concentration in the part of the electron blockinglayer 200 d adjacent to the 2DHG inducing layer 140 is about 10¹⁹atoms/cm³. The Al intensity of the 2DHG inducing layer 140 is greaterthan the Al intensity the electron blocking layer 200 d, which indicatesthat the aluminum concentration of the 2DHG inducing layer 140 isgreater than the aluminum concentration the electron blocking layer 200d. The Al intensity of the electron blocking layer 200 d is greater thanthe Al intensity of the active layer 130, which indicates that thealuminum concentration of the electron blocking layer 200 d is greaterthan the aluminum concentration of the active layer 130, including thewell layers 134 and the barrier layers 132. The Al intensity of the 2DHGinducing layer 140 is greater than the Al intensity of the n-typesemiconductor layer 110, which indicates that the aluminum concentrationof the 2DHG inducing layer 140 is greater than the aluminumconcentration of the n-type semiconductor layer 110. The Ga intensity ofthe 2DHG inducing layer 140 is less than the Ga intensity of electronblocking layer 200 d, and is less than the Ga intensity of the n-typesemiconductor layer 110. The gallium concentration of the 2DHG inducinglayer 140 is less than a gallium concentration of electron blockinglayer 200 d, and is less than a gallium concentration of the n-typesemiconductor layer 110.

FIG. 15 is an energy band diagram of the ultraviolet C light-emittingdiode of FIG. 13. Referring to FIG. 13 and FIG. 15, the physicalmeanings of the curves respectively corresponding to E_(c), Ef_(n),E_(v), and Ef_(p) as well as the unit “eV” in FIG. 15 are described inthe paragraph explaining FIG. 5, and are not repeated herein. Besides,the curve corresponding to p with unit “cm⁻³” in FIG. 15 means the holedensity. It can be learned from FIG. 15 that the 2DHG inducing layer 140induces 2DHG, and thus electron holes are generated inside the 2DHGinducing layer 140. Therefore, the p curve has a peak inside the 2DHGinducing layer 140 corresponding to high electron hole density. As aresult, electron holes from the 2DHG inducing layer 140 are injected tothe active layer 130. Therefore, the light efficiency of the ultravioletC light-emitting diode 100 d is effectively improved. By adopting the2DHG inducing layer 140, the extra electric holes carrier injectionefficiency of the ultraviolet C light-emitting diode 100 d under acurrent density of 35 ampere per cm² is increased from 10% (without the2DHG inducing layer 140) to 30% (with the 2DHG inducing layer 140) frombandgap structure simulation.

FIG. 16A is a curve of carrier injection efficiency of the ultraviolet Clight-emitting diode of FIG. 13 with respect to α−γ when the electronblocking layer has a Mg concentration of 10¹⁹ atoms/cm³. FIG. 16B is acurve of carrier injection efficiency of the ultraviolet Clight-emitting diode of FIG. 13 with respect to α−γ when the electronblocking layer has a Mg concentration of 10¹⁹ atoms/cm³. FIG. 16A andFIG. 16B are simulated under a current density of 35 ampere per cm².FIG. 16A shows that when the electron blocking layer 200 d has Mgconcentration of 10¹⁹ atoms/cm³, 2DHG is formed under the condition of0.2≤α−γ≤0.3. When 2DHG is formed, carrier injection efficiency will beincreased. In FIG. 16A, the carrier injection efficiency of α−γ=0.2 isslightly higher than the carrier injection efficiency of α−γ=0.1, whichindicates that the 2DHG begins to be formed when α−γ=0.2. The carrierinjection efficiency of α−γ=0.3 is even higher than the carrierinjection efficiency of α−γ=0.2, which indicates that the phenomenon of2DHG becomes stronger. FIG. 16B shows that when the electron blockinglayer 200 d has Mg concentration of 10²⁰ atoms/cm³, 2DHG is formed underthe condition of 0.1<α−γ≤0.3. The Mg concentration of electron blockinglayer 200 d in FIG. 16B is higher than that in FIG. 16A, the increase incarrier injection efficiency of 0.2≤α−γ becomes even more apparent inFIG. 16B than that in FIG. 16A. The higher the Mg concentration ofelectron blocking layer, the more 2DHG be generated in 2DHG inducinglayer 140. In FIG. 16, the carrier injection efficiency of α−γ=0.2 ismuch higher than the carrier injection efficiency of α−γ=0.1, whichindicates that the 2DHG begins to be formed when 0.1<α−γ.

FIG. 17 is an image of transmission electron microscopy (TEM) of theultraviolet C light-emitting diode in FIG. 13. Referring to FIG. 13 andFIG. 17, it can be learned from FIG. 17 that the 2DHG inducing layer 140forms a bright white line, which means high transparency. The more thealuminum concentration in the 2DHG inducing layer 140, the more thetransmittance of the 2DHG inducing layer 140 for light having awavelength of 230 nm to 280 nm. When the cation molar fraction ofaluminum in the n-type semiconductor layer 110 changes from 49% to 60%,the transmittance of the n-type semiconductor layer 110 for light havingthe wavelength of 230 nm to 280 nm changes from 0% to 76.3%. Inaddition, the aluminum concentration of the 2DHG inducing layer 140 maybe greater than the aluminum concentration of the n-type semiconductorlayer 110, and thus the transmittance of the 2DHG inducing layer 140 forlight having the wavelength of 230 nm to 280 nm may be greater than76.3%. The transparency of the 2DHG inducing layer 140 makes the 2DHGinducing layer 140 less absorb the light emitted from the active layer130.

Each film layer of the ultraviolet C light-emitting diode of eachembodiment of the disclosure may be fabricated by adopting a metalorganic chemical vapor deposition (MOCVD) process or other suitablesemiconductor manufacturing process, which is known to those of ordinaryskill in the art and therefore will not be described in detail herein.

In summary, in the ultraviolet C light-emitting diode of the embodimentof the disclosure, since it is designed that the concentration ofmagnesium in the second electron blocking layer is greater than theconcentration of magnesium in the first electron blocking layer, and theconcentration of magnesium in the second electron blocking layer isgreater than 10¹⁸ atoms/cm³, through the doping of magnesium in aspecific ratio relationship (for example, the above-mentioned magnituderelationship and numerical range regarding magnesium concentration, and,for example, the magnesium concentration distribution curves in FIG. 2and FIG. 9), it is possible to effectively suppress the electrons in theactive layer from overflowing to the p-type semiconductor layer, therebyimproving the element performance of the ultraviolet C light-emittingdiode. The ultraviolet C light-emitting diode in the embodiment of thedisclosure adopts a 2DHG inducing layer and satisfies α>γ and0.1<α−γ≤0.3, so that 2DHG is formed at the interface between the 2DHGinducing layer and the electron blocking layer. The induction of 2DHGfacilitates electron holes to be directly injected into the active layer130, so that the light efficiency of the ultraviolet C light-emittingdiode 100 d is effectively improved.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of thedisclosed embodiments without departing from the scope or spirit of thedisclosure. In view of the foregoing, it is intended that the disclosurecover modifications and variations of this disclosure provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. An ultraviolet C light-emitting diode,comprising: an n-type semiconductor layer; a p-type semiconductor layer;an active layer, disposed between the n-type semiconductor layer and thep-type semiconductor layer, wherein a wavelength of a maximum peak of aspectrum emitted by the active layer ranges from 230 nm to 280 nm; atwo-dimensional hole gas (2DHG) inducing layer, disposed between theactive layer and the p-type semiconductor layer, wherein a material ofthe 2DHG inducing layer comprises Al_(α)Ga_(β)N, β=1−α, and aconcentration of magnesium in the 2DHG inducing layer is less than 10¹⁷atoms/cm³; and an electron blocking layer, disposed between the p-typesemiconductor layer and the 2DHG inducing layer, wherein a material ofthe electron blocking layer comprises Al_(γ)Ga_(δ)N, δ=1−γ, 0.65<γ≤0.9,and a concentration of magnesium in a part of the electron blockinglayer adjacent to the 2DHG inducing layer is greater than 10¹⁹atoms/cm³, wherein α>γ and 0.1<α−γ≤0.3, so that 2DHG is formed at aninterface between the 2DHG inducing layer and the electron blockinglayer.
 2. The ultraviolet C light-emitting diode of claim 1, wherein0.7<α≤0.95.
 3. The ultraviolet C light-emitting diode of claim 1,wherein 0.2·α−γ≤0.3.
 4. The ultraviolet C light-emitting diode of claim1, wherein the concentration of magnesium in the part of the electronblocking layer adjacent to the 2DHG inducing layer is greater than 10²⁰atoms/cm³.
 5. The ultraviolet C light-emitting diode of claim 1, whereinthe active layer is a multiple quantum well layer comprising a pluralityof well layers and a plurality of barrier layers stacked alternately,and the 2DHG inducing layer is in contact with one of the well layersclosest to the 2DHG inducing layer.
 6. The ultraviolet C light-emittingdiode of claim 5, wherein an aluminum concentration of the electronblocking layer is greater than or equal to an aluminum concentration ofthe well layers.
 7. The ultraviolet C light-emitting diode of claim 5,wherein an aluminum concentration of the electron blocking layer isgreater than or equal to an aluminum concentration of the barrierlayers.
 8. The ultraviolet C light-emitting diode of claim 1, wherein athickness of the 2DHG inducing layer ranges from 1 nm to 3 nm.
 9. Theultraviolet C light-emitting diode of claim 1, wherein a ratio of athickness of the electron blocking layer to a thickness of the 2DHGinducing layer ranges from 6 to
 20. 10. The ultraviolet C light-emittingdiode of claim 1, wherein for light emitted by the active layer,transparency of the 2DHG inducing layer is greater than transparency ofthe electron blocking layer.
 11. The ultraviolet C light-emitting diodeof claim 10, wherein for the light emitted by the active layer, thetransparency of the 2DHG inducing layer is greater than transparency ofthe n-type semiconductor layer, and the transparency of the n-typesemiconductor layer is less than the transparency of the electronblocking layer.
 12. The ultraviolet C light-emitting diode of claim 10,wherein for light emitted by the active layer, the transmittance of the2DHG inducing layer is greater than 76.3%.
 13. The ultraviolet Clight-emitting diode of claim 1, wherein a refractive index of the 2DHGinducing layer is less than a refractive index of the electron blockinglayer.
 14. The ultraviolet C light-emitting diode of claim 1, wherein arefractive index of the 2DHG inducing layer is less than a refractiveindex of n-type semiconductor layer.
 15. The ultraviolet Clight-emitting diode of claim 1, wherein an electrical resistivity ofthe 2DHG inducing layer is greater than an electrical resistivity of theelectron blocking layer.
 16. The ultraviolet C light-emitting diode ofclaim 1, wherein an aluminum concentration of the 2DHG inducing layer isgreater than an aluminum concentration of the n-type semiconductorlayer.
 17. The ultraviolet C light-emitting diode of claim 1, wherein agallium concentration of the 2DHG inducing layer is less than a galliumconcentration of electron blocking layer, and is less than a galliumconcentration of the n-type semiconductor layer.
 18. The ultraviolet Clight-emitting diode of claim 1, wherein the electron blocking layercomprises: a first electron blocking layer; and a second electronblocking layer disposed between the 2DHG inducing layer and the firstelectron blocking layer, wherein a concentration of magnesium in thesecond electron blocking layer is greater than a concentration ofmagnesium in the first electron blocking layer, and the concentration ofmagnesium in the second electron blocking layer is greater than 10¹⁹atoms/cm³.
 19. The ultraviolet C light-emitting diode of claim 18,wherein the concentration of magnesium in the second electron blockinglayer is greater than 10²⁰ atoms/cm³.
 20. The ultraviolet Clight-emitting diode of claim 1, wherein a concentration of magnesium inthe active layer is less than 10¹⁷ atoms/cm³.